In contrast to the quasi-crystals previously documented, which can only be produced under special laboratory conditions, they are simply structured polymers that evolve through self-assembly.
(A) Defraction image of a colloidal quasi-crystal with 12-fold symmetry; underneath the corresponding tiling. - (B) Defraction image of a colloidal quasi-crystal with 18-fold symmetry; again underneath the corresponding tiling. - The tilings depict the respective complete overall structures. Images: Department of Physical Chemistry, University of Bayreuth; free for publication when references are included.
Due to their structural characteristics, they will probably be used in the development of innovative devices in photonics. In the "Proceedings of the National Academy of Sciences of the United States of America (PNAS)", the participating scientists from Bayreuth, Zurich, Hamburg and Grenoble report this discovery.
Unusual symmetrical structures, made visible in diffraction experiments
Quasi-crystals are characterised by a very unusual alignment of atoms. In normal crystals, atoms form ordered periodical structures; i.e. they arrange themselves into a gap-free integral overall structure, whereby one single symmetrical pattern is regularly repeated. For geometrical reasons, only 1-, 2-, 3-, 4- and 6-fold symmetries are possible. This figure indicates how frequently a structure may be rotated between 0 and 360 degrees, until it is congruent with itself. Quasi-crystals behave differently. They contain ordered aperiodic structures, i.e. there are at least two different symmetrical patterns which form a gap-free integral overall structure, despite not repeating themselves regularly. Under these circumstances, 8-, 10- or 12-fold symmetries may originate.
The structural differences between crystals and quasi-crystals can be made visible in diffraction experiments, using electromagnetic waves. This results in diffraction patterns that provide information on the structure of crystals and quasi-crystals. The discernible symmetrical structures are termed diffraction symmetries.
Colloidal quasi-crystals that evolve through self-assembly
The colloidal quasi-crystals that were discovered are hydrogels (insoluble water-containing polymers). They have a relatively simple structure and evolve by self-assembly of identical "building bricks". Such "building bricks" are polymer micelles: small spherical entities with a diameter ranging between 5 and 100 nanometres, which can be produced on a greater scale without any laboratory input. Therefore colloidal quasi-crystals are easily obtainable to a great number of scientists and to industry.
Professor Stephan Förster's Bayreuth University team has been studying polymer micelles capable of forming lattice structures (i.e. on scales of up to 100 nanometres length) for a considerable period. In joint research projects with the Institute Laue-Langevin in Grenoble and the DESY in Hamburg, it was recently discovered that from such self-assembly, quasi-crystalline lattice structures may evolve. Not only was a 12-fold symmetry observed in diffraction experiments, but also an 18-fold symmetry for the very first time.
Perspectives for innovative uses in photonics
Such experiments are under no circumstances to be considered "glass bead games" of fundamental research. Researchers in the field of photonics, a branch of physics, are interested in high-numbered diffraction symmetries applied to the development of optical technologies for the transfer and saving of information. In recent years it was shown that structures with high diffraction symmetries are characterised by the passage of light rays only in certain directions. They are a particularly suitable medium when it comes to the passage of light rays of a certain wavelength in previously defined directions. Therefore structures with high diffraction symmetries are extremely relevant to the manufacture of photonic devices.
Are the recently discovered hydrogels, with their high diffraction symmetries, suitable as "building materials" for photonics? For this to happen, one obstacle needs to be overcome: photonics requires structural characteristics of several hundred nanometres, while colloidal quasi-crystals do not extend beyond 100 nanometres. Scientists in Bayreuth, Hamburg and Grenoble are currently intensively working on the formation of quasi-crystalline larger structures, suitable for use in photonic devices, from polymer micelles. "I am optimistic that such endeavours will soon be successful", says Professor Stephan Förster.
Quasi-crystals – no longer a laboratory curiosity
Colloidal quasi-crystals are expected to be far more suitable for uses within photonics than the approx. 100 quasi-crystalline compounds known to date. These are nearly all metal alloys that can only be produced in small amounts and under special laboratory conditions. Furthermore, these quasi-crystalline structures range in size between 0.1 and 1 nanometre. For practical use in photonics, they are first and foremost far too small. In order to produce quasi-crystalline structures for photonics, up until now very intricate electrolithographic processes were required. The very existence of quasi-crystals was first proven in 1984 by a research team fronted by the American physicist Dan Shechtman. Afterwards, quasi-crystals were considered a laboratory curiosity for a long period, until photonics researchers were alerted to their unusual structural characteristics.
The international research team now publishing their discovery of colloidal quasi-crystals, includes Stephan Förster and his Bayreuth University team, Professor Walter Steurer and Dr Sofia Deloudi (ETH Zurich), Dr Peter Lindner (ILL Grenoble) and Dr Jan Perlich (DESY Hamburg).
Publication:Steffen Fischer, Alexander Exner, Kathrin Zielske, Jan Perlich, Sofia Deloudi, Walter Steurer, Peter Lindner, Stephan Förster,
Christian Wißler | Universität Bayreuth
Further reports about: > Colloidal > DESY > PNAS > Photonics > Proceeding > Proceedings of the National Academy of Sciences > Quasi-Crystals > aperiodic structures > crystalline structure > electrolithographic processes > electromagnetic wave > electromagnetic waves > high-numbered diffraction symmetries > photonic devices > symmetrical structures
Climate cycles may explain how running water carved Mars' surface features
02.12.2016 | Penn State
What do Netflix, Google and planetary systems have in common?
02.12.2016 | University of Toronto
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
02.12.2016 | Medical Engineering
02.12.2016 | Agricultural and Forestry Science
02.12.2016 | Physics and Astronomy